Excluded volume effect and orientational ordering near charged surface in solution of ions and Langevin dipoles

The influence of a finite volume of ions and orientational ordering of water Langevin dipoles on the dielectric permittivity profile in the vicinity of charged surface is studied theoretically via a numerical solution of the modified Poisson–Boltzmann equation. It is shown that the dielectric permittivity profile close to the charged surface is mainly determined by two mechanisms; specifically, the depletion of dipoles at the charged surface due to accumulated counterions and the increased orientational ordering of the water dipoles.